<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<script type="text/javascript" src="http://cdn.bootcss.com/jquery/2.1.4/jquery.min.js">

</script>

	<script type="text/javascript">
	function cloneli() {
		var li = $('li').eq(0).clone();
		$('ul').append(li);
	}
	</script>
</head>
<body>
	
	<form action="3.php" method="post" enctype="multipart/form-data">
		<input type="file" name="icon">
		<ul>
			<li>
				<input type="file" name='up[]'>
				<span onclick='cloneli()'>[+]</span>
			</li>
		</ul>
		<br>
		<input type="submit" value="上传">
		
	</form>
	

</body>
</html>